A significant amount of energy used in domestic households is consumed in heating water. For example water is heated for personal washing, showering and bathing, and for washing in the laundry and kitchen. In many of these domestic applications, heated water is drained away to waste after use while still at a temperature elevated above the temperature of the incoming cold water fed to the household. This can represent a significant wastage of energy.
European Patent No. 513,705 “Heat exchanger for waste water piping” shows a heat exchanger with tubing helically wrapped about the pipe of a waste trap under a hand basin.
German Patent Application No. 196 08 404 “Shower waste water residual heat recovery” shows a heat exchanger built into a sloping sub-floor under a shower base. Waste water flows down the sloping floor.
New Zealand Patent No. 250784 “Heat recovery system for shower” describes a heat recovery system that is built into the base of a shower. Incoming cold water is fed through a heat exchanging pipe that is distributed across a substantial portion of the shower base.
United Kingdom Patent Application No. 2,295,666 “Shower using waste heat” describes a waste trap formed of inner and outer concentric tubes that together are arranged in a spiral pattern under the floor pan of a shower. The inner tube, which may be corrugated, feeds water to the shower while the outer tube drains waste water from the shower.
United Kingdom Patent Application No. 2,342,146 “Heat exchanger” describes a heat exchanger that is connected into the outlet from a waste trap under a shower base. Heat transferred from the shower waste water pre-heats fresh water being fed to the shower.
United Kingdom Patent Application No. 2,385,785 “Domestic shower waste water heat exchanger” describes a heat exchanger that is fitted in the drain pipe of a bath having a shower overhead. Heat from the waste water preheats the supply to the shower.
United Kingdom Patent Application No. 2,389,373 “Shower waste trap” describes a shower waste trap having a central waste water chamber surrounded by a jacket through which incoming cold water is fed. The jacket has baffles arranged in a spiral pattern which are said to direct water evenly around the heat exchanger, increase the surface area in contact with the cold water and strengthen the exchanger.
U.S. Pat. No. 4,300,247 “Energy conservation in shower bathing” describes a heat exchanger located under a shower base. The exchanger pre-heats incoming cold water with hot drain water. Incoming cold fresh water and hot drain water are forced to follow serpentine paths in opposite directions on opposite sides of a folded sheet, e.g. of copper.
U.S. Pat. No. 4,619,311 “Method and apparatus for recovering heat in waste water” describes a heat exchanger which has been marketed as the GFX (gravity film exchange) water heater booster. This device has also been described in “Award-Winning GFX Water Heater Booster” at http://gfxtechnology.com and in “Inventions and Innovation—Success Story”, at http://www.eere.energy.gov/inventions/pdfs/waterfilm.pdf.
The GFX system uses a double-walled vented copper pipe to recover heat energy from wastewater to preheat incoming water, and is said to work while the drain and supply lines are in concurrent use, for example when someone is having a shower. Cold water fed through a tube wound spirally around a vertical waste pipe is preheated and passed simultaneously to the shower mixer and to the hot water storage cylinder.
U.S. Pat. No. 5,857,515 “Heat exchanging device” describes a finned heat conductive exchanger (eg of aluminium) which is fitted in the wall of a waste water pipe (eg of PVC). A cold water feed pipe (eg of copper) is in thermal contact with the heat exchanger. In a typical implementation, the waste pipe carries heated waste water from a shower and the cold feed pipe carries water which is eventually mixed with the a warm water supply for the shower. The cold feed is thus preheated by heat recovered from the shower waste water.
These prior art arrangements do not describe a waste trap heat exchanger that is easily accessible for cleaning and/or that can be readily retrofitted in the base or floor tray of an existing shower installation.